Rubocop crashes on ternary with empty else when in auto-correct mode

[rpherbig]

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---

Expected behavior

Running rubocop in auto-correct mode should behave the same as normal mode, but also fix as many issues as possible. This is the output in normal mode:

$ rubocop temp.rb
Inspecting 1 file
W

Offenses:

temp.rb:2:1: C: Use %w or %W for an array of words.
['a', 'b', 'c'].each_with_index do |name, index|
^^^^^^^^^^^^^^^
temp.rb:2:37: W: Unused block argument - name. If it's necessary, use _ or _name as an argument name to indicate that it won't be used.
['a', 'b', 'c'].each_with_index do |name, index|
                                    ^^^^
temp.rb:3:3: C: Favor the ternary operator (?:) over if/then/else/end constructs.
  if index > 2 then next else end
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
temp.rb:3:26: C: Redundant else-clause.
  if index > 2 then next else end
                         ^^^^
temp.rb:5:14: C: Final newline missing.
puts 'finish'


1 file inspected, 5 offenses detected

Actual behavior

However, rubocop crashes on the same script in auto-correct mode:

$ rubocop --auto-correct temp.rb
Inspecting 1 file


0 files inspected, no offenses detected
undefined method `type' for nil:NilClass
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/style/one_line_conditional.rb:52:in `requires_parentheses?'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/style/one_line_conditional.rb:48:in `expr_replacement'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/style/one_line_conditional.rb:44:in `ternary'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/style/one_line_conditional.rb:38:in `replacement'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/style/one_line_conditional.rb:26:in `block in autocorrect'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/corrector.rb:57:in `call'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/corrector.rb:57:in `block (2 levels) in rewrite'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/parser-2.3.1.2/lib/parser/source/rewriter.rb:194:in `transaction'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/corrector.rb:56:in `block in rewrite'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/corrector.rb:54:in `each'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/corrector.rb:54:in `rewrite'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/team.rb:145:in `autocorrect_all_cops'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/team.rb:77:in `autocorrect'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/team.rb:105:in `block in offenses'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/team.rb:122:in `investigate'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/team.rb:101:in `offenses'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cop/team.rb:52:in `inspect_file'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/runner.rb:223:in `inspect_file'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/runner.rb:193:in `block in do_inspection_loop'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/runner.rb:183:in `loop'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/runner.rb:183:in `do_inspection_loop'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/runner.rb:93:in `block in file_offenses'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/runner.rb:103:in `file_offense_cache'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/runner.rb:91:in `file_offenses'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/runner.rb:82:in `process_file'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/runner.rb:59:in `block in inspect_files'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/runner.rb:57:in `each'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/runner.rb:57:in `inspect_files'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/runner.rb:35:in `run'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cli.rb:72:in `execute_runner'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/lib/rubocop/cli.rb:28:in `run'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/bin/rubocop:14:in `block in <top (required)>'
c:/Ruby200/lib/ruby/2.0.0/benchmark.rb:296:in `realtime'
c:/Ruby200/lib/ruby/gems/2.0.0/gems/rubocop-0.42.0/bin/rubocop:13:in `<top (required)>'
c:/Ruby200/bin/rubocop:23:in `load'
c:/Ruby200/bin/rubocop:23:in `<main>'

Steps to reproduce the problem

I made a simple ruby file that demonstrates the problem. Run rubocop on it twice to see the problem (once normally, once with auto-correct):

puts 'start'
['a', 'b', 'c'].each_with_index do |name, index|
  if index > 2 then next else end
end
puts 'finish'

Running it shows it is a valid Ruby script:

$ ruby temp.rb
start
finish

RuboCop version

Include the output of rubocop -V:

$ rubocop -V
0.42.0 (using Parser 2.3.1.2, running on ruby 2.0.0 i386-mingw32)

[Drenmi]

Hm. EmptyElse should definitely take precedence here, but we could probably make OneLineConditional a bit smarter so it doesn't register an offense for incomplete if, else clauses.